SUMMARY OF SEVERAL RECENT CHONDRITE FINDS FROM THE TEXAS PANHANDLE     

Paul S. Sipiera  Edward J. Olsen  Dorothy L. Eatough  Bruce D. Dod 《Meteoritics & planetary science》1983,18(1):63-75

Eleven recent chondrite finds from the Texas Panhandle have been examined and classified according to mineralogical and petrological criteria: five H's, five L's, and one LL chondrite. Five are distinct from nearby finds, while three remain ambiguous and three are related to previously reported chondrites. In addition, data are provided to classify the Muleshoe, Silverton, and Vigo Park chondrites, all of which were previously undescribed in the literature.  相似文献   

Young stellar populations in the local group: an HST and GALEX comprehensive study     

L. Bianchi  Y. B. Kang  B. Efremova  D. Thilker  P. Hodge  P. Massey  K. Olsen 《Astrophysics and Space Science》2011,335(1):249-255

The study of the stellar constituents of star-forming sites in a wide variety of conditions yields the key to interpreting wide-field UV-optical imaging of extended nearby galaxies, and of distant galaxies. We obtained six-band imaging (from far-UV to I) with HST-WFPC2 of 67 sites of recent star formation in eight Local Group galaxies. HST pointings were selected from GALEX wide-field FUV imaging, which traces the young stellar populations. The HST observations were optimized to characterize the hottest, most massive stars in these regions. From the HST photometry, analyzed with stellar model colors, we derived the physical parameters of the massive stars in each field, and of the extinction by interstellar dust. The HST results are used to interpret GALEX UV measurements of SF across the entire galaxies. Our comprehensive photometric study at HST resolution (sub-pc scale in these galaxies) also provides an ideal selection of targets for follow-up spectroscopy with large ground-based telescopes, and in the UV with HST- or WSO-class telescopes, to clarify the influence of metallicity on the properties and the evolution of massive stars.  相似文献   

Climate-driven changes in water level: a decadal scale multi-proxy study recording the 8.2-ka event and ecosystem responses in Lake Sarup (Denmark)     

Rikke Bjerring  Jesper Olsen  Erik Jeppesen  Bjørn Buchardt  Jan Heinemeier  Suzanne McGowan  Peter R. Leavitt  Renée Enevold  Bent V. Odgaard 《Journal of Paleolimnology》2013,49(2):267-285

A two-stage change in lake level during the 8.2-ka event was identified in Lake Sarup, Denmark (55°N), using a multiproxy approach on precise radiocarbon wiggle-matched annually laminated sediments deposited 8740–8060 cal. yr BP. Changes in δ¹³C and δ¹⁸O indicated closed lake hydrology driven by precipitation. The isotopic, sedimentary and plant macrofossil records suggested that the lake level started to decrease around 8400 cal. yr BP, the decrease accelerating during 8350–8260 before an abrupt increase during 8260–8210. This pattern shows that the climate anomaly started ~150 years before the onset of the 8.2-ka cooling event registered in Greenland ice cores, but was synchronous with hydrologic change in the North American Lake Agassiz drainage. The lake level decrease was accompanied by a higher accumulation rate of inorganic matter and lower accumulation rates of cladoceran subfossils and algal pigments, possibly due to increased turbidity and reduced nutrient input during this drier period. Pigment analysis also showed added importance of diatoms and cryptophytes during this climate anomaly, while cyanobacteria became more important when the water level rose. Moreover, Nymphaeaceae trichosclereids were abundant during the period of algal enrichment. Cladoceran taxa associated with floating leaved plants or benthic habitats responded in a complex way to changes in water level, but the cladoceran assemblages generally reflected deep lake conditions throughout the period. The lake did not return to its pre-8.2-ka event status during the period of analysis, but remained more productive for centuries after the climatic anomaly as judged from the pigment accumulation and assemblage composition. The change to more eutrophic conditions may have been triggered by erosion of marginal deposits. Together, these data confirm the chronology of hydrologic changes and suggest, for the first time, that lake levels exhibited both a decline and an increase in rapid succession in response to the 8.2-ka event in southern Scandinavia.  相似文献   

Accuracy and efficiency of stencils for the eikonal equation in earth modelling     

Tor Gillberg  ?yvind Hjelle  Are Magnus Bruaset 《Computational Geosciences》2012,16(4):933-952

Motivated by the needs for creating fast and accurate models of complex geological scenarios, accuracy and efficiency of three stencils for the isotropic eikonal equation on rectangular grids are evaluated using a fast marching implementation. The stencils are derived by direct modelling of the wave front, resulting in new and valuable insight in terms of improved upwind and causality conditions. After introducing a method for generalising first-order upwind stencils to higher order, a new second-order diagonal stencil is presented. Similarly to the multistencil fast marching approach, the diagonal stencil makes use of nodes in the diagonal directions, whereas the traditional Godunov stencil uses solely edge-connected neighbours. The diagonal stencil uses nodes close to each other, reaching upwind, to get a more accurate estimate of the angle of incidence of the arriving wave front. Although the stencils are evaluated in a fast marching setting, they can be adapted to other efficient eikonal solvers. All first- and second-order stencils are evaluated in a range of tests. The first test case models a folded structure from the Zagros fold belt in Iran. The other test cases are constructed to investigate specific properties of the examined stencils. The numerical investigation considers convergence rates and CPU times for non-constant and constant speed first-arrival computations. In conclusion, the diagonal stencil is the most efficient and accurate of the three alternatives.  相似文献   

Mediterranean Seagrass Growth and Demography Responses to Experimental Warming     

Ylva S. Olsen  María Sánchez-Camacho  Núria Marbà  Carlos M. Duarte 《Estuaries and Coasts》2012,35(5):1205-1213

We experimentally examined the effects of increased temperature on growth and demography of two Mediterranean seagrasses Posidonia oceanica and Cymodocea nodosa. Shoots of C. nodosa and seedlings and shoots of P. oceanica were kept in mesocosms for 3?months and exposed to temperatures between 25 and 32?°C encompassing the range of maximum summer seawater temperatures projected for the Mediterranean Sea during the twenty-first century. The response of P. oceanica seedlings to warming was evident with reduced growth rates, leaf formation rates and leaf biomass per shoot. Younger life stages of P. oceanica may therefore be particularly vulnerable to climate change and warming. Leaf formation rates in the shoots of P. oceanica declined with increasing temperature and the lowest population growth (?0.005?day^?1) was found at 32?°C. Temperature effects on C. nodosa were variable. Rhizome growth increased with warming (0.07?C0.09?cm?day^?1?°C of warming), whereas other indicators of plant performance (aboveground/belowground biomass, leaf biomass and population growth) appeared to be stimulated by increased temperature to a threshold temperature of around 29?C30?°C beyond which they declined. P. oceanica and C. nodosa are likely to be negatively impacted by the effects of global warming over the next century and climate change poses a significant challenge to seagrasses and may stress these key habitat-forming species that are already suffering losses from anthropogenic impacts.  相似文献   

Distribution Coefficient of Trichloroethylene in Soil-Water Systems     

Mohsen Mehran  Roger L. Olsen  Bryan M. Rector 《Ground water》1987,25(3):275-282

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Book reviews     

Kenneth  H.  Olsen 《Geophysical Journal International》1989,99(3):817-818

Deep Drilling in Crystalline Bedrock, Volumes 1 and 2 A. Bodén and K. G. Eriksson ( eds ), Springer-Verlag , 1988, Volume 1: The Deep Gas Drilling in the Siljan Impact Structure, Sweden, and Astroblemes, xiv + 364 pp, ISBN 3-540-18995-5, $83.50 (DM138); Volume 2: Review of Deep Drilling Projects, Technology, Sciences and Prospects for the Future, xii + 538 pp, ISBN 3-540-18996-3, $102 (DM168).
Seismic strong motion synthetics Ed. B. A. Bolt
GPS Techniques Applied to Geodesy and Surveying. Lecture Notes in Earth Sciences, Vol. 19 E. Groten and R. Strauss ( eds )
Interpretation of filtered gravity maps F. Steiner and L. Zilahi-Sebess
Surface Waves and Discontinuities P. Malischewsky  相似文献   

Chondrule-like objects and brown glasses in howardites     

Edward J. Olsen  Kurt Fredriksson  Sundar Rajan  Albert Noonan 《Meteoritics & planetary science》1990,25(3):187-194

Abstract— Chondrule-like objects and brown glasses were analyzed in the howardites, Bununu, Malvern, Monticello, Pavlovka, and Yamato 7308. The objects are very similar to chondrules in ordinary and carbonaceous chondrites. Like the brown glasses the chondrule-like objects could have been produced by impact melting that left some crystalline nuclei, followed by a slower cooling rate than for the glasses. Alternatively, these objects are chondrules implanted from chondrite impactors. They are, however, without rims or any adhering matrix. The brown glasses appear to represent melting of average regolithic surface material, except for Monticello and Y7308, both of which have some siliceous glasses. The siliceous glasses could not have been produced by vapor fractionation but by melting of differentiated lithologies such as fayalitic granites. Impact mechanics indicates that howardites with abundant brown glasses came from an asteroid larger than Vesta (>400 km radius), upon which impacts occurred at relative velocities of up to 5 km/s. Howardites with little or no brown glasses came from a smaller parent body. We conclude that at least two parent bodies are likely sources for the basaltic achondrites.  相似文献   

Memorial for Louis H. Fuchs (1915–1991)     

Edward J. Olsen 《Meteoritics & planetary science》1992,27(1):106-106

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Sensitivity of the thermohaline circulation and climate to ocean exchanges in a simple coupled model   总被引：2，自引：0，他引：2  

G. Shaffer  S. M. Olsen 《Climate Dynamics》2001,17(5-6):433-444

 A new simple, coupled climate model is presented and used to investigate the sensitivity of the thermohaline circulation and climate to ocean vertical and horizontal exchange. As formulated, the model highlights the role of thin, ocean surface layers in the communication between the atmosphere and the subsurface ocean. Model vertical exchange is considered to be an analogue to small-scale, diapycnal mixing and convection (when present) in the ocean. Model horizontal exchange is considered to be an analogue to the effects of the wind-driven circulation. For small vertical exchange in the ocean, the model exhibits only one steady-state solution: a relatively cold, mid-high-latitude climate associated with a weak, salinity-driven circulation (“off ” mode). For large vertical and horizontal exchange in the ocean, the model also exhibits only one steady-state solution: a relatively warm, mid-high-latitude climate associated with a strong, thermally-driven circulation (“on” mode). For sufficiently weak horizontal exchange but large enough vertical exchange, both modes are possible stable, steady-state solutions. When model parameters are calibrated to fit tracer distributions of the modern ocean-atmosphere system, only the “on” mode is possible in this standard case. This suggests that the wind-driven circulation in consort with diapycnal mixing suppresses the “off ” mode in the modern ocean-atmosphere system. Since both diapycnal mixing and the wind-driven circulation would be expected to increase in a cold climate with greater meridional temperature gradients and enhanced winds, vertical and horizontal exchange in the ocean are probably associated with strong negative feedbacks which tend to stabilize climate. These results point to the need to resolve ocean wind-driven circulation and to greatly improve the treatment of ocean diapycnal mixing in more complete models of the climate system. Received: 16 November 1999 / Accepted: 19 June 2000  相似文献